1. Technical Field
This invention relates to a cover structure for internal combustion engines. More particularly, this invention relates to a cover structure for an internal combustion engine for covering a power transmission configured to transmit the power from a crank shaft to a cam shaft in the internal combustion engine.
2. Related Art
According to a known cover structure for internal combustion engines, the cover structure covers a power transmission (e.g., a timing chain) configured to transmit the power from a crank shaft to a cam shaft in an internal combustion engine. For instance, a cover structure 110 includes, as depicted in FIG. 19, a metallic cover member 111 attached to a main body 102 (e.g., cylinder block) of an internal combustion engine so as to cover a power transmission 105. The cover member 111 has an insertion hole 118 for a crank shaft 103, and the internal circumference of the insertion hole 118 of the cover member 111 holds an oil seal 112 pressurized onto the outer circumference of the crank shaft 103. However, since the cover structure 110 employs the cover member 111 made of a metal, the cover structure 110 has a greater weight. In order to reduce the weight, proposals have been made on a variety of cover structures for internal combustion engines where plastic cover members are employed (e.g., see JP-A-2015-102018 and JP-A-2015-071996).
JP-A-2015-102018 discloses a cover structure 210 having a plastic cover member 211 attached to a body 202 of an internal combustion engine so as to cover a power transmission (see, e.g., FIG. 20). In the above cover structure 210, the cover member 211 is provided with an insertion hole 218 for a crank shaft 203. The inner circumference of the insertion hole 218 of the cover member 211 holds an oil seal 212 pressurized to the outer circumference of the crank shaft 203, and the cover member 211 and the body 202 of the internal combustion engine are fastened by a fastening bolt 214. In this manner, the employment of the plastic cover member 211 contributes to the weight reduction, and the fastening bolt 214 suppresses the cover member 211 from being deformed by heat or the like.
On the other hand, JP-A-2015-071996 discloses a cover structure 310 having: a plastic cover member 311 attached to a body 302 of an internal combustion engine so as to cover a power transmission; and a metallic holding member 313 configured to hold an oil seal 312 pressurized to the outer circumference of the crank shaft 303 (see, e.g., FIG. 21). In this cover structure 310, the holding member 313 is fastened to the body 302 of the internal combustion engine by a fastening bolt 314 while partially covering the front side of the cover member 311. The cover member 311 and the holding member 313 sandwiches a gasket 345 positioned to surround the crank shaft 303. In this manner, the employment of the plastic cover member 311 and the metallic holding member 313 contributes to the weight reduction, and the metallic holding member 313 suppresses the cover member 311 from being deformed by heat or the like.
In the technique disclosed in JP-A-2015-102018, however, since the oil seal 212 is held by the inner circumference of the insertion hole 218 of the plastic cover member 211, it is difficult to meet the required dimension of the oil seal 212. More specifically, since the plastic cover member 211 is easily deformed in the radial direction of the crank shaft 203 due to a strained force, heat, pressure and creep of the oil seal 212, the sealing performance of the oil seal 212 is not sufficiently secured. Further, the fastening bolt 214 is difficult to be positioned in the neighborhood of the crank shaft, where the members such as a sprocket and pulley are centralized. In addition, another seal member 209 would be required to be positioned between the fastening bolt 214 and the cover member 211, which is also a hurdle for the positioning.
On the other hand, in the technique disclosed in JP-A-2015-071996, the gasket 345 located at an outer circumferential position is pressurized by bringing the metallic holding member 313 into contact with the plastic cover member 311. Thus, a dimensional tolerance is increased, and the compressibility of the gasket 345 is greatly varied. Further, the gasket 345 is positioned in the neighborhood of the oil seal 312. Since the gasket 345 is pressurized by the fastening bolt 314 located at an outer circumferential position, the gasket 345 is not sufficiently pressurized, and the gasket 345 does not exhibit sufficient sealing performance. Also, when the plastic cover member 311 is deformed by heat or pressure, the compressibility of the gasket 345 is reduced, which may lead to a leakage of oil. Moreover, the plastic cover member 311 is fastened to the body 302 of the internal combustion engine at a peripheral edge position, and then the metallic holding member 313 is fastened thereto at a peripheral edge position. Thus, the metallic holding member 313 has a greater size and a heavier weight.